What to get? Where to buy? Heat Treating
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Author:  Jason [ Sun Aug 13, 2006 6:31 pm ]
Post subject:  What to get? Where to buy? Heat Treating

I would like to be able to heat treat my stones at home but I havent a clue where to begin. I have seached the net and haven't found anything useful. I'm sure its out there but I dont know how to find it.

I'm not the kind of person who has to have shiny new everything so I would be willing to purchase used equipment. But, again, I dont know what i'm looking for. Can you tell me what i need to get to get started and the basic parameters of heat treating?


Author:  Doos [ Mon Aug 14, 2006 1:39 pm ]
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I don't believe it is that simple. Most of the recipes are secret and stay in the family.
Will be hard to find any information.

Author:  Jason [ Mon Aug 14, 2006 3:33 pm ]
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I'm not interested in anyones hard won recipies. I realize i'll have to experiment and learn by trial and error. Doesnt seem to me to be asking too much to want to know what kind of equipment to use.

Author:  JB [ Mon Aug 14, 2006 7:23 pm ]
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Try the link below. On the page that opens, click on "By Application" and then select gemstone heat treatment. A number of different furnace models will appear to select from.

I know nothing about this, but the type of gems you want to treat, the maximum temperatures the ovens can produce and the ability to control atmosphere in the oven will all play into it.

I don't think finding a furnace will be a problem. It's knowing what you are looking for, how you will use it, what to use it on, temperatures, cool downs, durations and atmospheres that will be the education.

Author:  Jason [ Mon Aug 14, 2006 9:05 pm ]
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Thanks for the link JB. Unfortunately all of those models seem to be quite industrial. But it is a neat site! :)

I am pretty frustrated in trying to find information. I understand why people wouldnt want to give up their knowledge on how to treat particular types of stones if they have had to gain that knowledge by trial and error. But I would think that if its such a big secret they would be willing to sell their services. Thus far I have not even found a heat treating service that will cater to the individual. And for that matter, I have only found one heat treating service PERIOD. And they require a minimum of a kilo of goods for an order.

I suppose I might as well just accept it as fact that this is not for me and get over it.


Author:  Snizzy [ Mon Aug 14, 2006 9:18 pm ]
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brimsjewelry wrote:

I suppose I might as well just accept it as fact that this is not for me and get over it.

Never give up on your dreams Jason! :smt115

Author:  Frank [ Tue Aug 15, 2006 10:22 am ]
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Hi Jason,

As JB said it depends on what you want to heat.

Some stones (like corundums) may have to be treated at temperatures up to around 1800-2000 degrees celsius. ...This is much hotter than a clay kiln ...hotter than many metal foundries use is therefore expensive. It costs hundreds of dollars to heat it up to temperature and keep it there (sometimes for days) at this temperature the furnace components have a very short life adding to the expence. No one wants to do this for anything less than a full furnace (hence the 1kg limit)... These furnaces cost tens of thousand of pounds.

Now lets say you want to heat some tanzanite or tourmaline...maybe colour change some amethyst? with this type of firing you can do it in a small test kiln of the type that will fire stoneware or porcelain. costs are much more suitable to small quantity firings.

As to where to go for information about temperatures etc...well there have been a few discusions on the forum over the months on the subject.
and if you have to start from scratch and develop your own recipes then we'll see how happily you give up your hard won secrets :)

Hope this is helpful


Author:  Jason [ Tue Aug 15, 2006 2:52 pm ]
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Thanks Frank,

This is exactly what I was looking for. Right now I want a kiln to heat treat tourmaline since thats what I have the most of. But, I had no clue whether a regular pottery or test kiln would do the job.


Author:  Aussie Sapphire [ Tue Aug 15, 2006 5:17 pm ]
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Hi Jason,

We keep out of heat treatment as much as possible but it's impossible over our years of playing with gemstones not to see, here and try different things. JB - that is a useful site, great looking gear with a price tag to suit ??

For stones that benefit from low heat, your test kiln or pottery kiln will work and is probably a good way if you are keen to learn and experiment. Remember you will have failures without knowledge so you may lose some valuable stone along the way.

I think Vincent said at one stage heat treatment started when man first sat in front of an open fire (or words to that affect) - he was meaning they simply placed stones in the fire to see what would result. I have placed our natural red zircon just in the coals in our fireplace and removed the red colour. Zircon seems to change at very low heat I guess 600 degrees Celcius but it's not a very stable change and over a period can regain some colour.

The problem with most of these cheaper kilns for corundum is they only go to 1150 degress or thereabouts - the silk in our Sapphire can disappear at around 1250 but 1100 isnt enough. Most corundums need around 1800.

As JB said once you need these higher temp ovens the cost is quite high. However I have seen some primitive "burners" that are little more than a small bricked in furnace, often heated with Coke and assisted with a blower. These work pretty well and are cheap to set up - you obviously dont have the fine control of a modern oven though. A partner of mine has told me of seeing one of these operating in Thailand in a multi story housing block, set up in the entire area of the fire escape with the bottom and top door prised open to create a chimney effect - dont try this at home :wink: .

If you are keen there are ways to learn - by experience is probably the best but there are still I think courses offered in Thailand to learn the basics (not sure of detail but someone may know - maybe have a look at Ted Themelis' website).

Author:  red dirt [ Wed Aug 16, 2006 1:14 am ]
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here's a two pdf links on heat treatment of corundums

Author:  Jason [ Wed Aug 16, 2006 4:11 pm ]
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Thanks folks,

You've been more than helpful. While I would love to be able to heat treat ruby and sapphire, it is unfortunately way out of budget. I'll be happy just to do tourmaline, beryl and quartz.

Again, thanks for the information and encouragement!


PS: I'll update as I get equipment and start experimenting.

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